In the processing of food within an oven, it has long been the most important desideratum that there be a uniform distribution of heated air within the oven to insure uniform heating or cooking of the food. Because an oven contains a relatively large volume of air, it has proven to be quite difficult to minimize temperature gradients and hot spots within the oven, and, consequently, to avoid the uneven application of heat to the food. There have been numerous attempts at such minimization of uneven cooking through oven designs wherein forced convection heating is utilized in an effort to attain temperature uniformity. These ovens have, in general, a heat source, such as a gas or electric burner, and a blower which draws air to be heated across the heat source to heat it and discharges the air thus heated into the cooking chamber.
In U.S. Pat. No. 4,928,663 of Nevin et al there is shown a forced convection oven wherein air heated in a combustion chamber is directed into a blower assembly, which also receives air from the oven chamber which is mixed with the heated air, and the mixture is forced out into the oven chamber. Thus, the blower assembly mixes currents or streams of air, one of which is introduced into the blower assembly from the front and the other of which is introduced through the rear, and centrifugally discharges the uniform temperature mixture into the oven chamber. This is in contrast to the more common arrangement where the two streams are mixed in the oven compartment where the food is located.
In U.S. Pat. No. 5,016,606 of Himmel et al. the air is heated by a burner externally of the oven and delivered to a blower by means of a fire tube. The blower mixes the air so delivered with return air from the oven chamber and discharges the mixture into the oven chamber. In U.S. Pat. No. 4,071,738 of Jenn et al, the air is heated after it is blown into the oven chamber, thus the oven of this patent utilizes both radiant heating and convection heating, inasmuch as the burners or heaters are within the oven chamber, however, the use of heating units within the cooking chamber, as shown by Jenn et al. limits such use to electrical heating elements.
Another type of convection heating oven utilizes jets of heated air applied to the food being cooked. Such ovens are shown in U.S. Pat. Nos. 4,474,498 of Smith and 4,626,661 of Henke, while U.S. Pat. No. 4,817,509 of Erickson discloses an arrangement where heated air is swirled over the food, which is placed in close proximity to the blower. Another arrangement utilizing a swirling action is shown in U.S. Pat. No. 4,865,864 of Rijswijck. In some instances, the nature of the food being cooked, such as certain types of bread, for example, is such that jets of air or swirling air can adversely affect or disturb the food. Thus, it is desirable, in most cases, that there be a general circulation of uniform temperature air which does not disturb the food. The aforementioned Nevin et al patent is directed to such a heating arrangement.
In all of the foregoing, with the exception of the Jenn et al patent, radiant heating is not utilized, or it is not a serious factor in the cooking process. Thus, even though the prior art patents are aimed, in most cases, at achieving uniformity of temperature throughout the volume of the oven, they do not utilize radiant heating to supplement the convection heating with a consequent economy of operation of the oven. In addition, prior art arrangements utilizing forced convection heating, in general, apply the heated air directly to the blower from the rear, thus all of the heated air is under forced convection. Such ovens require somewhat elaborate ducting to distribute the heated air more or less evenly and to return the air to the burner or heater.